Sheets of steel are used in a multitude of applications where strength, durability and ease of manufacture are required at low cost. For example, sheets of steel are used in vehicle bodies, appliances, furniture, construction and packaging. An important measure of a sheet steel's performance is its resistance to elastic deflection, otherwise known as stiffness.
For applications where high stiffness is needed, the thickness of sheet steel must be increased proportionately to the stiffness requirements. The extra material thickness provides additional resistance to elastic deflection. However, increasing the sheet steel's thickness negatively impacts both the cost and weight of the final product.
Thus, while the cost of steel is significantly lower than the cost of aluminum, aluminum has become the material of choice for applications where the weight of the final product is critical. Still more reductions in weight are achieved in construction materials comprising aluminum composite panels having a polymer core and outer metal skins made of aluminum sheet. Such panels find application, for example, in the construction of vehicular trailer bodies as disclosed in U.S. Pat. No. 4,958,472 and U.S. Pat. No. 4,940,279.
It has been recognized that the increased strength-to-weight ratio achieved in such composite panels results from the physical separation of the outer skins, and that a filler material or core material may not be required. In WO96/23621, it is proposed to create hollow panels in which a separation between two sheets of steel is maintained by hemispherically shaped domes formed in one sheet of steel which is selectively welded to an adjacent sheet of steel.
On the other hand, applicant is not aware of any proposals to maintain stiffness in composite panels by substituting alternative core materials for polymer cores. Applicant is also unaware of any proposals to create laminated structural panels in which the outer skins are made of steel. Those applications in which metal laminated to paper are known include inter alia metal clad wiring cards to support electronic components such as in U.S. Pat. No. 4,314,002 where paper is used because of its contribution to dielectric properties and provides no structural advantage. In other known metal and paper laminates, such as wrapping materials disclosed in U.S. Pat. No. 3,055,768, the metal is a very thin aluminum foil which has no structural utility.
An object of this invention is to increase the stiffness of sheet metal for use in structural applications of the kind mentioned above, without adding excessive cost or weight.